The present disclosure relates to a biosensor system and method for accurately measuring an analyte in a bodily fluid, such as blood, wherein the system comprises a unique process and system for distinguishing between the application of a test control solution and an actual sample. For example, the present disclosure provides a system and method for preventing a biosensor from erroneously identifying a control solution as an actual patient/user sample.
Electrochemical sensors have long been used to detect and/or measure the presence of substances in a fluid sample. For example, sensors have been used to detect the presence of one or more analytes in a fluid. The one or more analytes may include a variety of different substances, which may be found in biological samples, such as blood, urine, tears, semen, feces, gastric fluid, bile, sweat, cerebrospinal fluid, saliva, vaginal fluid (including suspected amniotic fluid), culture media, and/or any other biologic sample. The one or more analytes may be found in nonbiologic samples as well, such as food, water, wine, pool chemistry, soil, gases, and/or any other nonbiologic sample. In the most basic sense, electrochemical sensors comprise a reagent mixture containing at least an electron transfer agent (also referred to as an “electron mediator”) and an analyte specific bio-catalytic protein (e.g. a particular enzyme), and one or more electrodes. Such sensors rely on electron transfer between the electron mediator and the electrode surfaces and function by measuring electrochemical redox reactions. When used in an electrochemical biosensor system or device, the electron transfer reactions are transformed into an electrical signal that correlates to the concentration of the analyte being measured in the fluid sample.
The use of such electrochemical sensors to detect analytes in bodily fluids, such as blood or blood derived products, tears, urine, and saliva, has become important, and in some cases, vital to maintain the health of certain individuals. In the health care field, people such as diabetics, for example, have a need to monitor a particular constituent (e.g. glucose) within their bodily fluids. A number of systems are available that allow people to test a body fluid, such as, blood, urine, or saliva, to conveniently monitor the level of a particular fluid constituent, such as, for example, cholesterol, proteins, and glucose. Patients suffering from diabetes, a disorder of the pancreas where insufficient insulin production prevents the proper regulation of blood glucose levels, have a need to carefully monitor their blood glucose levels on a daily, or even more frequent, basis. A number of systems that allow people to conveniently monitor their blood glucose levels are available. Such systems typically include a test strip where the user applies a blood sample and a meter that “reads” the test strip to determine the glucose level in the blood sample. Diligent testing and controlling blood glucose levels by diabetics can reduce the risk of serious damage to the eyes, nerves, and kidneys as well as lower the risks of some forms of cardiovascular disease.
An exemplary electrochemical biosensor is described in commonly-assigned U.S. Pat. No. 6,743,635 ('635 patent) which is incorporated by reference herein in its entirety. The '635 patent describes an electrochemical biosensor used to measure glucose level in a blood sample. The electrochemical biosensor system is comprised of a test strip and a meter. The test strip includes a biosensor formed of a sample chamber, a working electrode, a counter electrode, and fill-detect electrodes. A reagent layer is disposed in the sample chamber. The reagent layer contains an enzyme specific for glucose, such as, glucose oxidase or glucose dehydrogenase, and a mediator, such as, potassium ferricyanide or ruthenium hexaamine. When a user applies a blood sample to the sample chamber on the test strip, the reagents react with the glucose in the blood sample. The meter applies a voltage to the electrodes to cause electrochemical redox reactions. When an appropriate potential is applied between the working electrode and the counter electrode, the electron mediator is oxidized, thereby generating a current that is related to the glucose concentration in the blood sample. The meter measures the resulting current that flows between the working and counter electrodes and calculates the glucose level based on current measurements.
Because of variations inherent in the biosensor manufacturing process, test strips do not perform identically. Therefore, it is necessary to calibrate the measuring instrument, such as, for example a meter, in a lot-specific manner. This is nowadays carried out automatically by means of lot-specific codes that are read by the measuring instrument or are entered into the measuring instrument by the user. The code is then used by the meter software to automatically adjust and calibrate the algorithm used by the meter to evaluate the electrical measurements.
Lot-specific differences are often due to the manufacturing processes and differences in the chemical reagent layer. In addition, measuring instruments are also subject to variations in their measuring accuracy. For example, measurement inaccuracy can result from prolonged or inappropriate storage of the test strips. In addition, inaccuracies can also result from improper meter usage by the operator. Hence, it is necessary to carry out a functional and quality control of the measuring system at regular intervals in order to detect and, if necessary, eliminate calibration errors in the instrument itself. For these purposes, manufacturers of measuring systems offer control liquids for use with a measuring system. The control liquids are usually essentially composed of aqueous, buffered solutions of the subject analyte in a known, predetermined concentration.
The control solutions are most often applied by a user when using a particular meter for the first time, when using a test strip from a new lot for the first time, after the meter has been dropped (or otherwise subject to potential damage), or when the previous results displayed from a sample do not seem to match usual or expected results. A control test can also be performed on a periodic basis. When performing a test with the control solution, most meters require that a user perform a certain initial test protocol, such as entering a specific code, or pressing a particular button or key on the meter. This initial protocol alerts the meter that the following results are indicative of the control solution and not the results of an actual patient sample. Based on the control solution test results, the meter will then properly calibrate its measurement algorithm as necessary to compensate for measurement inaccuracies.
Properly indicating the occurrence of a control solution test is important for the proper operation of the meter as well as for maintaining a proper patient test history. In some meters, the patient's test history, including the time of testing and sample results, is recorded in memory and used as underlying data to warn the user, according to certain preset alert conditions. If a user fails to accurately notify the meter when a control solution test is being administered, the meter will erroneously record the result as a valid patient test result (as opposed to merely a control solution). Such an oversight can lead to a number of problems, such as an inaccurate or incomplete patient record or history being recorded in the meter's memory. In turn, these inaccuracies can potentially lead to a dangerous situation where a doctor erroneously provides a diagnosis based on improper patient information.
Accordingly, there is a need in the field of measuring the concentration of a substance in a sample for a system and method that reduces the potential for improperly designating a control sample as an actual user/patient sample.